Force sensor for sensitive robots

Robots are commonplace in production halls, but are only allowed to operate in protected areas so as not to endanger humans with their movements. A new cost-efficient, robust force sensor can make robots sensitive to potential collisions.

The arm of the industrial robot steadily approaches the employee, who is so absorbed in his work that he does not notice – a risky situation. But as soon as the robot even slightly touches the person, it immediately retracts its steel arm. This vision could soon become reality thanks to a cost-efficient force and torque sensor developed by research scientists at the Fraunhofer Institute for Silicon Technology ISIT in Itzehoe, Germany.

Glued onto a steel plate – the transducer – it can be screwed in between the arm and the grabber. “We expect our sensors to be far cheaper than conventional force sensors once they enter mass production. This makes them suitable for wide-scale use,” says ISIT head of department Jörg Eichholz.

Equipped with the new sensors, robotic assistants would be sufficiently trustworthy to work alongside their human colleagues – something that has been prohibited until now for safety reasons. The sensor measures the forces and torques exerted by the robot arm. The element is made from a single square piece of silicon. On each side, bridges are incorporated which are carrying electrical resistances. These resistances work in a similar way to strain gauges. If the robot arm bumps into an obstacle, the shape of the silicon changes very slightly – by just a few micrometers, to be precise. This causes either more or less current to flow, depending on whether a bridge has been stretched or buckled.

The sensor can also help to program a robot. In the learning mode, it measures the force with which the employee guides the robot arm. Instead of laboriously entering the coordinates of the movements into the computer, the employee can simply guide the robot by touch, and teach it the required motion sequences in this way.

Fraunhofer Institute for Silicon Technology ISIT
Jörg Eichholz
joerg.eichholz@isit.fraunhofer.de
www.isit.fraunhofer.de